1. Field of the Invention
This invention relates to a disc cartridge having accommodated therein a disc on which predetermined information signals are recordable or have been recorded, such as a magneto-optical disc or an optical disc. More particularly, it relates to a disc cartridge provided with a shutter for opening and closing an aperture by means of which at least a part of a signal recording area of the disc may be radially exposed to an exterior environment.
2. Description of Related Art
There has previously been proposed a disc for recording and/or reproducing information signals, such as a magneto-optical disc or an optical disc. This disc is comprised of a disc-shaped base plate and a recording layer formed on at least one major surface of the base plate. The central portion of the disc is formed as a clamp area which is to be retained by a disc driving unit of a disc recording and/or reproducing apparatus adapted for recording and/or reproducing information signals on or from the disc. The portion of the disc lying around the clamp area is reserved as a signal recording area on or from which the information signals are recorded of read.
Referring to FIG. 1, there has hitherto been proposed a disc cartridge comprised of a cartridge body 103 and a shutter member 110 which is accommodated within the cartridge body 103 and the shutter member 110 with a view to preventing deposition of dust and dirt on a disc 102 or injuries thereto due to contact especially with user's hands or fingers as well as to facilitating handling of the disc 102. The disc 102 accommodated within the cartridge body 103 may be rotated therein by disc rotating means. Referring to FIG. 2, the major surface of the cartridge body 103 is formed with an aperture 107 by means of which at least a part of the signal recording area of the disc may be exposed to an exterior environment across its inner and outer peripheries. The information signals may be recorded and/or reproduced on or from the signal recording surface by means of the disc recording and/or reproducing apparatus, through the aperture 107.
The disc cartridge is provided with the shutter member 110 adapted for closing the aperture 107 during non-use the disc cartridge as shown in FIG. 1 for protecting the disc 101 by preventing intrusion of dust and dirt into the inside of the cartridge body 103. The shutter member 110 is provided with a shutter portion or plate portion 111 of a size large enough to close the aperture 107. The shutter portion 105 is formed with a opening 109 corresponding in size and shape to the aperture 107. The shutter member 110 is mounted by the cartridge body 103 for sliding along a lateral side of the cartridge body 103 by having its end face 113 supported by a corresponding lateral side of the cartridge body 103. The shutter member 110 is supported in this manner for sliding between a first position of closing the aperture 107 by the shutter portion 111 as shown in FIG. 1 and a second position of opening the aperture 107 with the aperture 109 then being in register with the aperture 107 as shown in FIG. 2, as disclosed for example in U.S. Pat. Nos. 4,714,973 and 4,685,017.
A recess 115 for guiding the shutter portion 111 is formed on a major surface of the cartridge body 103 in an area thereof corresponding to the travel passage of the shutter portion 105. The recess 115 is of a depth corresponding to the thickness of the shutter portion 111. Thus the upper surface of the shutter portion 111 is substantially flush with the major surface of the cartridge body 103 for the entire sliding stroke of the shutter member 110 with respect to the cartridge body 103.
Meanwhile, the shutter member 110 is constituted by bending a substantially rectangular metallic plate. The shutter member 110 may also be formed by bending a plate of synthetic resin or by integral molding of synthetic resin.
It is noted that, when the disc cartridge is loaded into the disc recording and/or reproducing apparatus, the shutter member 110 has its proximal end 113, supported by the corresponding lateral side of the cartridge body 103, thrust by shutter opening means, not shown, provided in the disc recording and/or reproducing apparatus, so that the shutter member 110 is slid from the above mentioned first position to the second position, as indicted by arrow c in FIG. 2.
When the shutter member 110 is slid in this manner by the disc recording and/or reproducing apparatus, the shutter member 111 is subjected to a tilting force relative to the sliding direction under a force of friction between the cartridge body 103 and the distal free end of the shutter portion 111. If the shutter portion 111 is shorter in length in a direction along a lateral side of the cartridge body 103 indicated by double-headed arrow a in FIG. 1 than in a direction normal to the aforementioned lateral side indicated by double-headed arrow b in FIG. 1, the shutter portion 11 tends to be tilted with respect to the sliding direction as indicated by arrow d in FIG. 1. Should the shutter portion 111 be tilted with respect to the sliding direction, the shutter member 110 can not be slid smoothly with respect to the cartridge body 103.
On the other hand, if the shutter portion 111 is shorter in length in the direction along the aforementioned one lateral side of the cartridge body 103 than in the direction normal thereto, the shutter portion 111 is extended a longer distance from its proximal end 113 towards its distal end, so that it becomes difficult to form the shutter portion 111 as a flat plate.
For this reason, the shutter portion 111 is longer in the direction along the aforementioned one lateral side of the cartridge body 103, that is, in the sliding direction of the shutter member 110, than in the direction normal to the sliding direction of the shutter member 110. Above all, if the shutter portion 111 iS formed of synthetic resin, since the shutter portion 111 is lower in toughness than if the shutter portion is formed of metal , it becomes more necessary that the shutter portion 111 be longer in the direction along its sliding direction than in the direction normal thereto.
However, if the shutter portion 111 has a longer length in its sliding direction, the proportion of the area taken up by the shutter section guide recess 115 to the entire area of the major surface of the cartridge body 103 is necessarily increased. If the proportion of the area taken up by the shutter guide recess 115 is increased in this manner, it becomes difficult to provide the major surface with a so-called positioning holes or to apply a label on the major surface. These positioning holes are used for securing the disc cartridge in position within the disc recording and/or reproducing apparatus, while the label are used for indicating the contents of information signals recorded on the disc 102.
On the other hand, if the length in the sliding direction of the shutter portion 111 is increased as described above, there may arise a risk that the cartridge body 103 be correspondingly increased in size. That is, since the distance by which the shutter member 110 can be slid relative to the cartridge body 103 is determined by the size of the aperture 107 formed in the cartridge body 103, if the shutter portion 111 is of a longer length in the sliding direction of the shutter member 110, there may arise the risk that, when the shutter member 110 is slid relative to the cartridge body 103, the shutter portion 111 be protruded beyond the corresponding lateral side of the cartridge body 103.